Mine fuse safing system

ABSTRACT

The regulator of a fuze timing clock includes an electrical switch, which utilizes the breathing action of a balance wheel hairspring and a single or double stator contact. The switch produces a series of timing pulses which are dependent upon the number of stator contacts used and the period of the breathing action of the hairspring. In a fuze, the pulses can operate a self-sterilization circuit which will place the fuze in an unarmed or nonfiring condition. In such a fuze, power is fed to the output section of the fuze only when there is a continuous series of sustaining pulses from the electrical switch. Cessation of these pulses causes the sterilization circuit to turn off the output section gate thus removing power from the output of the fuze.

I United States Patent [1113,568,601

[ Inventor wflmll 3,115,834 12/1963 Schwarz et a1 102/18 sil Sp ng, Md. 3,384,017 5/1968 Lazarus et al 102/702 [21] P 747381 Primary Examiner-Verlin R. Pendegrass [22] Filed July 26,1968 A" H M S Ed d K n H b Patented Mar 9, 1971 orneysarry aragovltz, war J. e y, er ert Berl and J. D. Ed erton [73] Assignee The United States of America as represented g by the Secretary of the Army ABSTRACT: The regulator of a fuze timing clock includes an electrical switch, which utilizes the breathing action of a [54] G YSTEM balance wheel hairspring and a single or double stator contact. gmgs' Theswitch d f .1

pro uces a series 0 timmg pu ses WhlCh are depen [52] US. Cl. 102/702, dent upon the number of stator contacts used and the period 102/10, 102/1 of the breathing action of the hairspring. In a fuze, the pulses [51 Int. Cl. F42C l5/l0 an o rat a self-sterilization circuit which will place the fuze [50] Field of Search 58/28, in an unarmed or nonfiring condition, In such a fuze, power is BS: & 8, 10; 102/ l 8, 84 fed to the output section of the fuze only when there is a continuous series of sustaining pulses from the electrical switch. [56] References CM Cessation of these pulses causes the sterilization circuit to turn I E STATES PATENTS off the output section gate thus removing power from the out- 1,911,062 5/1933 Conrad 58/28 (A) put Ofthe fill t Patented March 9, 1971 3,568,601

2 Sheets-Sheet 1 FIG. 1

25 FUZE CONTROL CIRCURT INVENTOR WARREN R MORROW ,M We z-wmwa j} ATTORN EYS MEJE FUSE SAFWG SYSTEM BACKGROUND OF THE INVENTION in a mine fuze it is extremely important that the arming system perform its function in such a manner as to minimize dangers to the person or persons initiating the arming cycle. With recoverable mines there is the additional need for a reliabie sating system to restore the fuze to a positively unarmed condition, either from a fully armed state, an unknown state or one dependent upon self-controlled processes within the fuze.

Self-sterilization (hereafter referred to simply as sterilization) is defined as the process of placing the fuze in an unarmed or nonfiring condition through purely internal processes, such as completion of a timing cycle. While arming, safing, and steril zation are distinct processes, they are obviously functionally interrelated, and as a practical matter utilize the same subsystems in whole or in part. To this end, fuze design normally has redundancy between and within subsystems.

The basic sterilization philosophy is one of electrical and mechanical redundancy to enhance safety. Normally sterilization is accomplished both by direct mechanical action at the end of the sterilization period (i.e. closing a switch), and by circuitry which monitors clock motion and inhibits fuze activation upon cessation of clock motion even if the desired active period has not elapsed.

Previous methods of monitoring such a clock, which is normally a spring-wound mechanism, have used mechanical means placed at the lower end of the gear train of the clock. Available torque in this area is quite small, and designing the clock mechanisms which can provide the additional mechanical energy requires larger and heavier main springs. Additionally, the load applied by the monitoring system to the clock mechanism must absorb exactly the right amount of energy or the clock accuracy will be affected.

it is therefore an object of this invention to provide an electrical switch to monitor a fuze timer mechanism which absorbs no mechanical energy from the timer.

An additional object of the invention is to provide an electrical switch to monitor a fuze timer mechanism which will produce a pulse train in response to timer operation.

Still another object of the invention is to provide an electrical switch to monitor a fuze timer mechanism which will be inexpensive, lightweight and will occupy a minimum of space.

SUMMARY OF THE INVENTION An electrical switch to monitor the timer action in a mine fuze utilizing the breathing action of a balance wheel hairspring and a double or single stator contact. The electrical switch produces a series of pulses and cessation of these pulses due'to clock stoppage will activate a self-sterilization process within the fuze.

BRlEF DESCRIPTION OF THE DRAWINGS The specific nature of the invention'aswell as other objects, aspects, uses, and advantages thereof will clearly appear from the following description and from the accompanying drawing, in which:

FIG. it illustrates an electrical switch in accordance with my invention.

MG. 2 is a functional block diagram of a mine fuze using the switch of FIG. 3 in accordance with my invention.

DESCRlPTION OF THE PREFERRED EMBODIMENT PEG. it shows a clock mechanism having a shaft 243 with a balance wheel 12 fixed thereon and one end 22 of hairspring id connected to the shaft in close proximity to the balance wheel l2. One end it? of the shaft Ell is connected to a geared power train (not shown) to provide the energy for driving the balance wheel 12 and hairspring ill. End 24 of the hair spring it?) is connected to a fixed terminal 1% which also functions as an electrical contact for the conducting portion of hairspring iii. Hairspring stator contacts and M are connected to a terminal box 27 having an energy source therein and an output 25 connected to a fuze control circuit. While double stator contacts are shown it is equally possible to use only a single contact.

If the balance wheel 12 and spring 10 were part of a standard four beat per second timer, the electrical switch would produce 2 switch cycles per second with a single stator contact and four switch cycles per second with double stator contacts. As the balance wheel 12 rotates first in one direction and then in the other, the hairspring ill will contract and expand. The breathing action causes hairspring ill to make contact with the hair spring stator contacts 15 and 16 thus closing a circuit comprising the power source and terminal box 27, the portion of the hairspring 10 going between the stator contact and terminal l8 and the fuze control circuit. The output across terminals l8 and 25 will be a series of pulses, a pulse being produced every time the hairspring it! makes contact with one of the stators 115 or 16. i

The fuze circuit illustrated by a block diagram in H6. 2 is a mine fuze having a sensor 30 which provides a DC output signal when it senses an object in proximity to the mine, an amplifier 32 and in inverter 33 which amplifies and inverts this signal before sending it to a decision circuit 35. The decision circuit 35 is a simple two-transistor circuit which, while not a true peak detector, fires soon after the peak is passed. Since the decision circuit 35 requires a push-pull low-impedance drive, the amplifier 32 and inverter 33 provide the required drive and utilize feedback to maintain stable performance characteristics over a wide temperature range. Substantially, the amplifier 32 gain control provides a control of fuze sensitivity.

The firing circuit 37 accepts a high-impedance voltage level change from the decision circuit 35 and then discharges an energy-storing capacitor contained. therein through the detonator dill which will ignite the explosive in the mine. Because the firing circuitry 37 presents a low resistance across which a minimum voltage normally about 1.5 volts must be developed for reliable firing, the firing circuitry must be designed to be an efiicient switch with low impedance in the armed state. At the same time, the firing system must not trigger spuriously due to unwanted electrical or mechanical influences, and must be adaptable to fail-safe sterilization.

The DC power supply 44 is connected to the input section l7 and output section 48 of the fuze: through an arming and safe switching system 46. The arming system is a manual control located on the fuze case which performs the dual functions of operating an arming switch to stop or start fuze circuit operation, and releasing or rewinding the sterilizer mechanism. Turning the arming switch to the ON position will connect electrical power to the timer circuit 42, starting its operation.

The timer 42 consists of a standard clock mechanism and the electrical switch described in FIG. 1 to monitor its operation. When the arming switch 46 is turned on, the clock mechanism in timer 42. begins to run and the electrical switch starts generating pulses indicating clock motion. These pulses are sent to the sterilization circuitry 3%.

Because the input section 47 of the fuze depends for operation on the establishment of proper charge levels in several electrolytic capacitors, the time constants involved are necessarily large. it is important, therefore, that power be applied or removed from the input section only when the detonator at) is out of line or the firing circuit is 37 is inoperative. The reason for this being that when the supply voltage M is applied or removed, the inevitable readjustment of charges causes spurious signals to be delivered to the peak detector, which in turn delivers an output to the tiring section. For this reason the timer d2 maintains the detonator in an out-of-line condition for a nominal 10-minute period after arming, then snaps a detonator ill into line and connects it electrically. The timer d2 continues to run for 2 hours, at which time a switch is closed, followed by the jamming and stoppage of clock motion.

The signals from timer 42 indicating motion of the clock and switch closure are connected to the sterilization circuitry 38. The primary function of the sterilization circuitry 38 is to allow activation of the fuze output section 48 in the presence of a train of pulses from the motion sensor electrical switch in the timer 42, and the shutdown of that section upon cessation of the pulse train. The output section 48 must not be reactivated if the clock restarts, unless the restart is due to manual rearming via the arming and safe switching device 46. It is apparent, therefore, that the arming process must produce a signal which places the sterilizing circuitry 38 in an operative condition. Another function of the sterilization circuitry 38 is to electrically protect against runaway firing train alignment, and against such conditions as permanent alignment due to gear train failure. Finally the sterilization circuitry 38 must include provisions for continuing fuze operation beyond the 24 hour period when manual selection of the nonsterilizing mode is made. The nonsterilizing mode may be chosen by manually switching a mode selector 50 which is connected to overcome the sterilizing'function of the sterilization circuitry 38. The mode selector 50 simply actuates a switch which makes the circuit connections necessary for sterilizing or nonsterilizing operation. For safety reasons it is necessary that mode selection be possible only before the fuze is armed and for this reason a mechanical interlock is provided between the controls. The interlock prevents any change in the mode selector 50 after the arming handle of switch 46 is moved from the safe position.

During normal operation of the fuze the clock mechanism in the timer 42 begins to run and the electrical switch monitoring the clock sends a pulse train signal to the sterilization circuitry 38. After establishment of steady state conditions in the input and output sections 47 and 48, the detonator 40 will snap into its'armed position and connect electrically so that a firing signal from firing circuit 37 would initiate operation of the fuze. After the timer has run its full active period the 24 hour switch will be closed by the clock mechanism and the sterilization circuit 38 will immediately discharge the trigger energy storage capacitor in the firing circuitry 37, thereby providing positive inhibition of fuze functioning. The clock is then stalled by a mechanical stop causing cessation of pulses from the electrical switch in the timer circuit 42. If, due to some malfunction of the clock mechanism, the timer ceased operation momentarily during the 24 hour active period, the pulses from the electrical switch would also cease and the sterilization circuitry 38 would similarly cause the tiring circuitry 37 to discharge to a nonfiring condition.

Because premature clock stoppage is the most probable mechanical failure mode, the pulse operated sterilization cir-. cuitry, which removes power from the firing circuit 37 upon clock stoppage, must exhibit a high degree of reliability. The electrical monitoring switch in timer 42 provides the needed reliability by actuating the sterilization circuitry with a positive indication to clock stoppage.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

I claim:

1. A mine fuze safing system for deactivating said fuze after a predetermined period or upon fuze malfunction, comprising:

a. a firing circuit that activates a detonator in response to a signal from a sensing circuit;

b. a clock mechanism set to operate tion of said fuze;

c. pulse generating means integral with said clock mechanism that produces a series of electrical pulses as long as said clock mechanism remains continuously operative; and

d. logic circuitry for receiving said series of electrical pulses from said pulse enerating means and delivers a signal to said firing CllCLll to render it inoperable upon the cessation of said pulses from said pulse generating means.

2. The invention according to claim 1 wherein said contact means include first stator means adapted to make contact with said hairspring when said hairspring is approaching in a fully expanded condition.

3. The invention according to claim 2 wherein said contact means include a second stator means adapted to make contact with said hairspring when said hairspring is approaching in a fully contracted condition.

4. The invention according to claim 1 wherein said clock mechanism comprises a hairspring having a breathing action associated therewith, and wherein said pulse generating means comprises contact means disposed so that the breathing action of said hairspring causes said hairspring to make periodic electrical contact with said contact means that produces said series of electrical pulses.

for the period of activa- 

1. A mine fuze safing system for deactivating said fuze after a predetermined period or upon fuze malfunction, comprising: a. a firing circuit that activates a detonator in response to a signal from a sensing circuit; b. a clock mechanism set to operate for the period of activation of said fuze; c. pulse generating means integral with said clock mechanism that produces a series of electrical pulses as long as said clock mechanism remains continuously operative; and d. logic circuitry for receiving said series of electrical pulses from said pulse generating means and delivers a signal to said firing circuit to render it inoperable upon the cessation of said pulses from said pulse generating means.
 2. The invention according to claim 1 wherein said contact means include first stator means adapted to make contact with said hairspring when said hairspring is approaching in a fully expanded condition.
 3. The invention according to claim 2 wherein said contact means include a second stator means adapted to make contact with said hairspring when said hairspring is approaching in a fully contracted condition.
 4. The invention according to claim 1 wherein said clock mechanism comprises a hairspring having a breathing action associated therewith, and wherein said pulse generating means comprises contact means disposed so that the breathing action of said hairspring causes said hairspring to make periodic electrical contact with said contact means that produces said series of electrical pulses. 